The purpose of this investigation is to elucidate the nature and functional role of negatively charged sites on muscle cell surfaces and more specifically to determine if sialic acid groups play any functional role in excitation or in excitation-contraction coupling in muscle cells. We are investigating the effects of a wide variety of multivalent cations on various parameters of the action potential, on resting potentials reduced to low values by exposure of cells to calcium free solutions, and on excitation-contraction coupling. Calcium ions affect all of these processes; some ions mimic the action of calcium in some respects, but not in others, presumably reflecting differences in the binding properties of the various sites. One ion in which we are particulary interested is ruthenium red, a hexavalent cation. This ion is of interest as a probe of calcium sites in part because it is so different from calcium in terms of size and charge, and partly because it can be localized under the electron microscope. Further, we are examining the effects of the enzyme, neuraminidase, on the interaction between muscle cells and these various cations in the hopes of identifying any role that surface sialic acid groups may have in muscle cell function. BIBLIOGRAPIC REFERENCE: Howell, J.N. and K.W. Snowdowne, The effects of ruthenium red on electrical parameters of frog sartorius muscle. Biophys. J., 15:255a (1975). Abstract.